US2248776A - Wave filter - Google Patents

Wave filter Download PDF

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Publication number
US2248776A
US2248776A US221721A US22172138A US2248776A US 2248776 A US2248776 A US 2248776A US 221721 A US221721 A US 221721A US 22172138 A US22172138 A US 22172138A US 2248776 A US2248776 A US 2248776A
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crystal
band
arm
electrodes
shunt
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US221721A
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Henry G Och
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AT&T Corp
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Bell Telephone Laboratories Inc
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Priority to US221721A priority Critical patent/US2248776A/en
Priority to US232067A priority patent/US2199921A/en
Priority to DEI65224D priority patent/DE742179C/de
Priority to CH215766D priority patent/CH215766A/de
Priority to FR858308D priority patent/FR858308A/fr
Priority to NL66164D priority patent/NL66164C/xx
Priority to BE435676D priority patent/BE435676A/xx
Priority to GB21991/39A priority patent/GB531662A/en
Application granted granted Critical
Publication of US2248776A publication Critical patent/US2248776A/en
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/0023—Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns, or networks having balanced input and output
    • H03H9/0095—Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns, or networks having balanced input and output using bulk acoustic wave devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/542—Filters comprising resonators of piezoelectric or electrostrictive material including passive elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/54—Filters comprising resonators of piezoelectric or electrostrictive material
    • H03H9/58—Multiple crystal filters
    • H03H9/60—Electric coupling means therefor
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/01—Frequency selective two-port networks
    • H03H7/17—Structural details of sub-circuits of frequency selective networks
    • H03H7/1708—Comprising bridging elements, i.e. elements in a series path without own reference to ground and spanning branching nodes of another series path
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/01—Frequency selective two-port networks
    • H03H7/17—Structural details of sub-circuits of frequency selective networks
    • H03H7/1741—Comprising typical LC combinations, irrespective of presence and location of additional resistors
    • H03H7/1775—Parallel LC in shunt or branch path

Definitions

  • This invention relates to selective wave transmission networks which use piezoelectric crystals as impedance elements and more particularly to unbalanced wave filters of the bridged-T type.
  • the principal object of the invention is to reduce the number of component elements required in unbalanced wave lters.
  • a feature of the invention is a filter of the bridged-T type in which the series arms of the T are constituted by a single piezoelectric crystal with divided electrodes.
  • the series arms of the T have consisted of a pair of reactance elements such as inductors or capacitors.
  • the series arms of the T are constituted by a single crystal element having a split electrode on one or both sides.
  • the shunt branch of the T and the bridging branch may comprise inductors or capacitors, or a combination of these, and may include one or more additional crystals. Capacitors may be connected in shunt at the ends of the crystal.
  • the component elements may bearranged and proportioned to provide wave iilters of the low-pass, high-pass, band-pass or band-elimination type.
  • Fig. 1 shows the general configuration of the network of the invention
  • Fig. 2 is a perspective view of the piezoelectric crystal element showing how the electrodes are placed;
  • Fig. 3 is an equivalent lattice-circuit for the network of Fig. 1;
  • Fig. 4 shows a band-pass lter in accordance with the invention
  • Fig. 5 is an equivalent lattice for the iilter of Fig. 4;
  • Fig. 6 represents the reactance characteristics of the line and diagonal branches of the lattice of Fig. 5;
  • Figq is a typical attenuation characteristic for the lter of Fig. 4.
  • Fig. 8 shows the reversed poling for the connections to the electrodes of the crystal in the circuit of Fig. 4;
  • Figs. 9, 10, and l1 show respectively the equivalent lattice, the reactance characteristics for the ranches and a typical attenuation characteristic for the filter of Fig. 8;
  • Fig. 12 isa composite network comprising the filters of Figs. 4 and 8 connected in tandem;
  • Fig. 13 shows the invention embodied in a lowpass lter
  • Fig. 14 is an equivalent lattice for the filter of Fig. 13;
  • Figs. 15 and 16 show respectively the reactance characteristics of the impedance branches and the attenuation characteristic for one distribution of the critical frequencies in the equivalent lattice of Fig. 14;
  • Figs. 17 and 18 show respectively the reactance characteristics of the branches and a typical attenuation characteristic for another distribution of the critical frequencies in the lattice of Fig. 14;
  • Fig. 19 is a band-elimination -iilter in accordance with the invention.
  • Figs. 20, 21 and 22 show respectively the equivalent lattice, the reactance characteristics of the impedance branches and a typical attenuation .characteristic for the ilter of Fig. 19;
  • Fig. 27 shows an alternative structurefor the filter of Fig. 23 in which the bridging branch includes a piezoelectric crystal element;
  • Fig. 28 shows another alternative circuit for the high-pass lter.
  • Figs. 29 and 30 show respectively the equivalent lattice and the reactance characteristics of the branches for the lter of Fig. 28.
  • Fig. 1 is a general schematic diagram of the circuit arrangement of the filters 0f the invention, which are of the bridged-T type.
  • the series arms of the T are constituted by a piezoelectric crystal X having four electrodes, two of which are connected to one terminal of the shunt impedance branch Z2 and the remaining two of which are connected, respectively, to an input terminal I and the corresponding output terminal 3.
  • 'Ihe bridging branch of the network is constituted by the impedance Z1.
  • Two equal capacitors C1, C1, designated by their capacitances, are connected in shunt at the ends of the crystal.
  • the impedances Z1 and Z2 may be of any degree of complexity and may comprise inductors, capacitors and additional crystals.
  • Suitable load impedances may be connected to the input terminals l, 2 and the output terminals 3, 4.
  • the ligure shows the unbalanced form of the network in which the path between terminals 2 and i may be grounded or otherwise fixed in potential.
  • the lter may, of course, be built in the balanced form.
  • the crystal X is preferably of quartz in the form ofv a relatively narrow rectangular plate cut perpendicular to the electrical axis of the crystal and with its length in the direction ofthe mechanical axis. Such a crystal will vibrate longitudinally when alternating potentials are applied to electrodes placed on the larger surfaces. Other well-known types of crystal cut may be used and, under certain conditions, they may be preferred.
  • the crystal shown in Fig. 1 is of the rectangular type described above but for convenience is shown in end elevation.
  • the crystal X is provided with two electrodes 5, 6 on one of the major faces and two oppositely disposed electrodes 1, 8 on the opposite face.
  • These electrodes may be of silver, aluminum or ⁇ other suitable metal, plated directly onto the crystal, and may be applied by plating the two surfaces all over and afterwards removing a narrow longitudinal strip of the plating along the center of each face. It is generally desirable also to remove narrow strips of the plating around the edges of the crystal.
  • the crystal vibrates in the longitudinal mode, it is preferably supported between two or more opposymmetrical lattice network to which it is equiva' lent.
  • the line branch of the equivalent lattice is equal to half of the impedance measured between termin-als I and 3 of Fig.
  • l and the diagonal branch is equal to twice the impedance measured between terminals I an-d 3 strapped together and terminal 2 or 4. It i-s apparent that the mechanical vibration of the crystal occurs for only one of these measurements, depending upon the poling of the crystal electrodes. Therefore, the impedance representing the piezoelectric properties of the crystal will appear in only one of the branches of the lattice. The electrode capacitance of the crystal, however, will appear in the other branch.
  • Fig. 3 shows the equivalent lattice for the poling shown in Fig. 1, where the interconnected electrodes are on the same side' of the crystal. For this case the crystal impedance appears in the diagonal branch.
  • the equivalent lattice comprises two similar line impedance branches Za each consisting of the electrode capacitance Cu, an impedance and the capacitance C1, all connected in parallel, and two similar 4diagonal impedance rbranches Zh each made up of an impedance 2Z2 in series with the crystal impedance, the latter being shunted by the capacitance C1.
  • two similar line impedance branches Za each consisting of the electrode capacitance Cu, an impedance and the capacitance C1
  • two similar 4diagonal impedance rbranches Zh each made up of an impedance 2Z2 in series with the crystal impedance, the latter being shunted by the capacitance C1.
  • the crystal impedance is represented by its equivalent circuit comprising the capacitance C0 shunted by a branch consisting of an inductance L in series with a second capacitance C.
  • the capacitance Co represents the simple electrostatic capacitance between a pair of oppositely disposed electrodes, such as 5 and 1.
  • the values of the capacitance C and the inductance L depend upon'the dimensions of the crystal and also upon its piezoelectric and elastic constants.
  • the values of the elements in the equivalent circuit for the crystal in terms of the dimensions of the crystal X, may be determined from the following formulas, assuming that the electrodes cover substantially the entire area of the two major faces of the crystal.
  • Z, w and t are, respectively, the length, width and thickness of the crystal measured in centimeters.
  • the remaining impedances in the lattice are the same as the corresponding ones in the bridged-T, multiplied by the numerical factors as indicated.
  • Fig. l If reversed poling is used in Fig. l, that is, if the connections to a pair of oppositely disposed electrodes, for example electrodes 6 and 8, are interchanged, the impedance representing the piezoelectric properties of the crystal will appear in the line impedance branch instead of in the diagonal branch of the equivalent lattice.
  • the arm consisting of the capacitance C and the inductance L will be removed from the diagonal branch Zt and placed in parallel with the electrode capacitance Cn in the line branch Za. The other component elements of the lattice will remain unchanged.
  • the filter will have transmission bands in the regions where Zn and Zh are of opposite sign and will Ihave attenuation bands where Za and Zb are of the same sign, with peaks of attenuation occurring at the frequencies where Za and Zb are equal.
  • these expressions also give .the impedance and propagation constant of the bridged-T network of Fig. 1.
  • the values of the various circuit elements of the lattice can be found from the resonant and anti-resonant frequencies of t'he Za and Zh branches by a direct application of R. M. Fos'ters reactance theorem given in the Bell System Technical Journal, vol. III, No. 2, April 1924, pages 259 to 267.
  • the values of the component el-ements in the bridged-T network of Fig. 1 are found by applying the numerical factors indicated. By a Iproper choice of component elements any one of a variety of filter characteristics may be obtained.
  • Fig. 4 is a schematic diagram showing a bandpass iilter.
  • the series arms of the T are pro vided by the crystal X1 which has the capacitors C1, C1 shunting its ends.
  • the capacitor C2 forms the bridging branch, and no additional shunt mpedance is required.
  • the poling shown in Fig. l is used for the connections to the electrodes of the crystal and since the two electrodes l and 8 on one side of the crystal are connected together they may be replaced by a single electrode 9 as shown.
  • the equivalent lattice, following Fig. 3, is given in Fig. 5.
  • the line impedance branch is a capacitance equal to the sum of Co, C1 and 2C2, and the diagonal branch is made up of a capacitance equal to Co plus C1 shunted by an arm representing the piezoelectric properties of the crystal and consisting of the inductance L in series with the capacitance C.
  • Fig. 6 represents the reactancefrequency characteristics of the line and diagonal branches of the lattice of Fig. 5.
  • the reactance of the line branch Za is that of a simple capacitance and is given by the solid-line curve.
  • the reactance of the diagonal branch Zb exhibits a resonance at the frequency f2 and an anti-resonance at the frequency fs.
  • the transmission band extends from f2 to fa because in this region the reactances Za and Zh are of opposite sign. At all other frequencies the filter will attenuate, since the reactances are of the same sign. At some frequency f1. on the lower side of the transmission band, the two curves cross, and a peak of attenuation will occur here.
  • a typical attenuation characteristic is shown symbolically in Fig. 7.
  • the magnitude of the capacitance C1 shunting each end of the crystal does not aiect the frequency of resonance f2 but it does determine the location of the anti-resonance frequency f3. Since the width of the transmission band is determined by the separation of these two frequencies the band width of the filter can therefore be adjusted by varying the value of this capacitance. As indicated by the arrows in Fig. 4, the capacitors C1, C1 may be made Variable for this purpose. The widest band is obtained when these capacitances are Zero, that is, when they are omitted from the circuit. As these capacitances are increased in value, the width of the band is decreased, and a band as narrow as desired may be obtained.
  • the capacitance C2 has its greatest effect on the location of the crossing point of the two reactance characteristics. Since the location of this point determines theplacing of the peak of attenuation, the peak may be adjusted by varying the magnitude of this capacitance. As indicated, the capacitor C2 may be made variable to adjust the location of the peak. If C2 is omitted the peak is relegated to Zero frequency and as the value of C2 is increased the peak is made to approach the lower cut-olf frequency f2.
  • the line branch of the equivalent lattice as shown in Fig. 9, comprises a capacitance equal to the sum of Cn, 2C3 and C4 shunted by an arm consisting of the inductance L in series with the capacitance C, and the diagonal branch is constituted by a capacitance equal to Co plus C4.
  • the reactance kcharacteristics of the line branch Za and the diagonal branch Zt are given, respectively, by the solid-line curve and the dotted-line curve of Fig. 10.
  • the attenuation characteristic as shown in Fig.
  • the capacitor C3 may be made variable to adjust the location of the attenuation peak and the end capacitors C4, C4 may be made variable to adjust the width of the transmission band.
  • An attenuation characteristic having a peak on each side of the transmission band can be obtained by connecting in tandem the lter of Fig. 4 and the filter ⁇ of Fig. 8.
  • the filters should have matching image impedances and the same transmission band.
  • Such a composite lter is shown in Fig. 12.
  • the two capacitors C1and C4 connected in parallel at the junction of the two sections may, of course, be replaced by a single capacitance equal to the sum of the two.
  • band-pass filters shown in Figs. 4 and 8 require a minimum number of component reactance elements. If the full band width is used, so that the end capacitors may be omitted, each filter requires only a single crystal and one capacitor. No inductors are required in the design.
  • the other filters described hereinafter are also very economical in their use of elements.
  • the network of Fig. 4 can be converted into a low-pass nlter by the addition of an inductance in the bridging branch, as shown in Fig. 13.
  • the series arms of the T are provided by the crystal X3, which is shunted at its ends by the capacitors Cs and Cs.
  • the bridging branch consists of the inductance L1 and a capacitance Cc connected in parallel.
  • the equivalent lattice is given in Fig. 14 and the reactance characteristics of the line and diagonal branches are given in Fig. 15.
  • the line branch is a simple anti-resonant circuit andthe diagonal branch has a resonance and an antiresonance.
  • the filter wiil freely transmit all frequencies lying below fs, the anti-resonance frequency of the diagonal branch.
  • the attenuation characteristic for this distribution of the critical frequencies will be as shown symbolically in Fig. 16.
  • An attenuation peak may be introduced by making the two anti-resonances coincide, at the frequency fa, as shown by the reactance characteristics of Fig. 17.
  • the cut-oli will now occur at the frequency fs where the diagonal branch resonates, and the peak will be located at the frequency fio, where the curves cross.
  • a typical attenuation characteristic is shown in Fig. 18.
  • the network of Fig. 13 can be converted into a band-elimination filter by the addition of an inductance L3 in the shunt arm of the T, as shown in Fig. 19.
  • the crystal X4 provides the series arms of the T and the capacitors Cs, Ca furnish the shunt capacitances.
  • the bridging branch consists of the inductance L2 and the capacitance C7 connected in parallel.
  • the equivalent lattice is shown in Fig. 20 and the reactance characteristics of the two branches are given in Fig. 21.
  • An additional resonance is introduced into the diagonal branch Zb, at the frequency h5, and the attenuation band will extend from this frequency to the lower resonance at fu.
  • the two anti-resonances are placed at the same frequency, fia, and the curves will ordinarily cross at two frequencies, such as f12 and f14, thus locating the peaks of attenuation as shown by the characteristic of Fig. 22'. If the two curves do not cross, the two peaks will coalesce and there will be a single peak located at the frequency of anti-resonance J13.
  • the network of Fig. 19 can be converted to a high-pass filter by arranging the inductance and the capacitance in the bridging branch in series instead of in parallel, as shown in Fig. 23 by the elements L4 and C9.
  • a shunting capacitor, represented by Cio is also sometimes required in the bridging branch.
  • the equivalent lattice is shown in Fig. 24 and the reactance characteristics of the branches are given in Fig. 25.
  • a resonance is introduced in the line branch, at the frequency fw, and the anti-resonance occurs at fm1.
  • the anti-resonance of the diagonal branch is made to coincide with the resonance of the line branch, and the upper resonance of the diagonal branch is placed at the anti-resonance of the line branch.
  • Fig. 26 gives a typical attenuation characteristic It is seen that the bridging branch Z1 of the filter of Fig. 23 has the same configuration as the equivalent electrical circuit for a crystal. In certain cases this branch can, therefore, be replaced by a crystal element Xs as shown in Fig. 27. 'I'he other elements in Fig. 27 are the same as those in Fig. 23, and the two networks can be designed to have identical attenuation characteristics.
  • Fig. 28 Another form of high-pass lter is shown in Fig. 28 in which the crystal X7 employs reversed poling and is shunted at its ends by the capacitors C13 and C13.
  • the capacitor C12 forms the bridging branch
  • the shunt branch is constituted by the capacitor C14 and the inductor Ls connected in series.
  • the equivalent lattice is given in Fig. 29 and the reactance characteristics of its branches in Fig. 30.
  • the line branch has a resonance at f2s, which determines the cutoff, and an anti-resonance at fzi which coincides with the resonance of the diagonal branch.
  • the peaks of attenuation occur at the frequencies fzi and 322 where the two curves cross.
  • the attenuation characteristic is of the same type as that shown in Fig. 26. It will be noted that this high-pass filter requires only one inductor and a single crystal element.
  • a wave filter of the bridged-T type having a pair of input terminals and a pair of output terminals, said lter comprising a piezoelectric crystal having two electrodes on one face and two other oppositely disposed electrodes on the opposite face, two of said electrodes being connected directly together and through a common shunt branch to an input terminal and an associated output terminal, and the remaining electrodes being connected respectively to the remaining terminals, and a bridging impedance branch connected between said remaining terminals, the dimensions of said crystal and the values of the reactance elements forming said bridging branch and said shunt branch being ⁇ proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies.
  • a wave filter of the bridged-T type comprising a symmetrical T network consisting of two equal series arms and an interposed shunt impedance branch connected between a pair oi input terminals and a pair of output terminals, and a bridging impedance branch connected between the outer terminals of said series arms, said series arms being constituted by a single piezoelectric crystal having a divided electrode on at least one side, and the dimensions of said crystal and the values of the reactance elements constituting said bridging branch and said shunt branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies.
  • a wave lter in accordance with claim 3 which includes equal capacitors connected in shunt at the ends of said crystal.
  • said bridging branch includes a capacitor and an inductor connected in series and said shunt branch includes a second inductor.
  • a wave filter of the bridged-T type comprising a pair of input terminals, a pair of output terminals, a bridging impedance branch including a capacitor connected between an input terminal and a corresponding output terminal, and a piezoelectric crystal having two electrodes on one face and a third electrode on the opposite face, said two electrodes being connected respectively to the terminals of said bridging branch, said third electrode being connected to the remaining input terminal and output terminal, and the dimensions of said crystal and the values of the reactance elements constituting said bridging branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies.
  • a wave lter comprising a pair of input terminals, a pair of output terminals, a bridging impedance branch including a capacitor connected between an input terminal and a corresponding output terminal, and a piezoelectric crystal having two electrodes on one face and two other electrodes on the opposite face, an electrode on one face and an electrode on the opposite face being connected respectively to the terminals of said bridging branch, the remaining electrodes being connected together and to the remaining input terminal and output terminal, and the dimensions of said crystal and the values of the reactance elements constituting said bridging branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies.
  • a wave filter having a pair of input terminals and a pair of output terminals, said filter comprising a piezoelectric crystal having two electrodes on one face and two other oppositely disposed electrodes on the opposite face, two of said electrodes on the same face of the crystal being connected together and through a shunt branch to an input terminal and an associated output terminal and the remaining electrodes being connected respectively to the remaining terminals, and a bridging impedance branch connected between said remaining terminals, the dimensions of said crystal and the values of the reactance elements forming said bridging branch and said shunt branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies.
  • a wave filter having a pair of input terminals and a pair of output terminals, said filter comprising apiezoelectric crystal having two electrodes on one face and two other oppositely disposed electrodes on the opposite face, two of said electrodes which are diagonally opposite to each other being connected together and through a shunt branch to an input terminal and an associated output terminal and the remaining electrodes being connected respectively to the remaining terminals, and a bridging impedance branch connected between said remaining terminals, the dimensions of said crystal and the values of the reactance elements forming said bridging branch and said shunt branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies.
  • a wave filter having a pair of input terminals and a pair of output terminals, said filter comprising a piezoelectric crystal having two electrodes on one face and two other oppositely disposed electrodes on the opposite face, two of said electrodes being connected together and through a shunt branch to an input terminal and an associated output terminal and the remaining electrodes being connected respectively to the remaining terminals, a bridging impedance branch connected between said remaining terminals, and equal reactance elements connected in shunt at the ends of said crystal, the dimensions of said crystal and the values of said equal reactance elements and the reactance elements forming said bridging branch and said shunt branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies.
  • a wave filter having a pair of input terminais and a pair of output terminals, said filter comprising a piezoelectric crystal having two electrodes on one face and two other oppositely disposed electrodes on the opposite face, two of said electrodes being connected together and through a shunt branch to an input terminal and an associated output terminal and the remaining electrodes being connected respectively to the remaining terminals, and a bridging impedance branch including a capacitor and an inductor connected between said remaining terminals, the dimensions of said crystal and the values of the reactance elements forming said bridging branch and said shunt branch being proportioned with respect to one another and with respect to two preassgned frequencies 4to provide a transmission band between said frequencies.
  • a wave nlter in accordance with claim -15 in which said capacitor and inductor are connected in series.
  • a wave filter in accordance with claim 15 in which said capacitor and inductor are connected in parallel.
  • each of said filters having a vpair of input terminals and a pair of output terminals and each of said filters comprising a piezoelectric crystal having two electrodes on one face and two other oppositely disposed electrodes on the opposite face, two of said electrodes being connected together and through a shunt branch to an input terminal and an associated output terminal and the remaining electrodes being connected respectively to the remaining terminals, and a bridging impedance branch connected between said remaining terminals, the dimensions of said crystal and the values of the reactance elements forming said bridging branch and said shunt branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies, said lters having the same transmission band, the interconnected electrodes in one of said lters being on the same side of the crystal and the interconnected electrodes in the other of said filters being diagonally opposite to each other.
  • a wave lter comprising a pair of input terminals, a pair of output terminals, a bridging impedance branch including a capacitor connected between an input terminal and a corresponding output terminal, and a piezoelectric crystal having two electrodes on one face and a third electrode on the opposite face, said two electrodes being connected respectively to the terminals of said bridging branch, said third electrode being connected to the remaining input terminal and output terminal, the dimensions of said crystal and the values of the reactance elements constituting said bridging branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies and said capacitor being made variable in order to adjust the location of a peak of attenuation in the attenuation characteristics of the lter.
  • a wave filter comprising a pair of input terminals, a pair of output terminals, a bridging impedance branch including a capacitor connected between an input terminal and a corresponding output terminal, a piezoelectric crystal having two electrodes on one face and a third electrode on the opposite face, and two equal capacitors, said two electrodes being connected respectively to the terminals of said bridging branch, said third electrode being connected to the remaining input terminal and output terminal, said equal capacitors being connected in shunt at the ends of said crystal, the dimensions of said crystal and the values of said equal capacitors and the reactance elements constituting said bridging branch being proportioned with respect to one another and with respect to two preassigned frequencies to provide a transmission band between said frequencies, and said equal capacitors being made variable in order to adjust the width of said transmission band.

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  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
  • Filters And Equalizers (AREA)
  • Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
US221721A 1938-07-28 1938-07-28 Wave filter Expired - Lifetime US2248776A (en)

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Application Number Priority Date Filing Date Title
US221721A US2248776A (en) 1938-07-28 1938-07-28 Wave filter
US232067A US2199921A (en) 1938-07-28 1938-09-20 Wave filter
DEI65224D DE742179C (de) 1938-07-28 1939-07-20 Wellenfilter nach Art einer ueberbrueckten T-Schaltung
FR858308D FR858308A (fr) 1938-07-28 1939-07-26 Filtres d'ondes électriques
CH215766D CH215766A (de) 1938-07-28 1939-07-26 Wellenfilter.
NL66164D NL66164C (en(2012)) 1938-07-28 1939-07-27
BE435676D BE435676A (en(2012)) 1938-07-28 1939-07-28
GB21991/39A GB531662A (en) 1938-07-28 1939-07-28 Wave filter

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US221721A US2248776A (en) 1938-07-28 1938-07-28 Wave filter
US232067A US2199921A (en) 1938-07-28 1938-09-20 Wave filter

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Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2988714A (en) * 1957-09-12 1961-06-13 Gen Electric Piezoelectric filter network
US3179906A (en) * 1965-04-20 By-pass netwoems when
US3284728A (en) * 1961-09-22 1966-11-08 Siemens Ag Electromechanical filter
US3613031A (en) * 1969-12-15 1971-10-12 Hughes Aircraft Co Crystal ladder network having improved passband attenuation characteristic
US3676806A (en) * 1969-11-06 1972-07-11 Gte Automatic Electric Lab Inc Polylithic crystal bandpass filter having attenuation pole frequencies in the lower stopband
US3686592A (en) * 1970-10-08 1972-08-22 Us Army Monolithic coupled crystal resonator filter having cross impedance adjusting means
US3697903A (en) * 1968-05-17 1972-10-10 Clevite Corp Equal-resonator piezoelectric ladder filters
US3704433A (en) * 1971-05-27 1972-11-28 Bell Telephone Labor Inc Band-elimination filter
US4028647A (en) * 1976-04-28 1977-06-07 Northern Telecom Limited Monolithic crystal filters
US4099149A (en) * 1977-04-15 1978-07-04 Northern Telecom Limited Single side band monolithic crystal filter
US4163959A (en) * 1977-12-15 1979-08-07 Motorola, Inc. Monolithic crystal filter device
US4207535A (en) * 1978-03-20 1980-06-10 Motorola, Inc. Two-pole, fixed-tuned monolithic crystal frequency discriminator
EP0020729A4 (en) * 1978-12-11 1981-05-15 E Systems Inc MONOLITHIC CRYSTAL FILTER NETWORK WITHOUT INDUCTOR.
US4281300A (en) * 1979-11-08 1981-07-28 Motorola, Inc. Multi-pole crystal filter and method of improving the frequency response
US5030934A (en) * 1989-07-05 1991-07-09 Motorola, Inc. Crystal notch filter comprising discrete quartz crystals coupled to a trimmable RC bridging network
US5051711A (en) * 1989-04-27 1991-09-24 Ten-Tec, Inc. Variable bandwidth crystal filter with varactor diodes
US20020167376A1 (en) * 2001-05-11 2002-11-14 Murata Manufacturing Co., Ltd. Piezoelectric filter
US20080293668A1 (en) * 1995-01-27 2008-11-27 Schinazi Raymond F [5-carboxamido or 5-fluoro]-[2',3'-unsaturated or 3'-modified]-pyrimidine nucleosides

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR861831A (fr) * 1939-08-08 1941-02-18 Materiel Telephonique Filtres d'ondes électriques
US2485863A (en) * 1946-01-05 1949-10-25 Western Electric Co Method of and apparatus for making electrical measurements
DE1223900B (de) * 1954-03-10 1966-09-01 Siemens Ag Aus mehreren, Resonanzkreise enthaltenden Filtergliedern bestehendes Bandpassfilter relativ schmalen Durchlassbereiches
NL112778C (en(2012)) * 1955-05-16
US2929031A (en) * 1957-02-06 1960-03-15 Hermes Electronics Co Intermediate band width crystal filter
NL283486A (en(2012)) * 1961-09-22
US3396327A (en) * 1961-12-27 1968-08-06 Toyotsushinki Kabushiki Kaisha Thickness shear vibration type, crystal electromechanical filter
US3564463A (en) * 1966-04-11 1971-02-16 Bell Telephone Labor Inc Monolithic piezoelectric filter having mass loaded electrodes for resonation regions acoustically coupled together
DE2001433C3 (de) * 1970-01-07 1983-06-01 Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka Bandpaßfilter
JPS5249618Y2 (en(2012)) * 1972-10-21 1977-11-11

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1967250A (en) * 1931-09-19 1934-07-24 Bell Telephone Labor Inc Wave filter

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3179906A (en) * 1965-04-20 By-pass netwoems when
US2988714A (en) * 1957-09-12 1961-06-13 Gen Electric Piezoelectric filter network
US3284728A (en) * 1961-09-22 1966-11-08 Siemens Ag Electromechanical filter
US3697903A (en) * 1968-05-17 1972-10-10 Clevite Corp Equal-resonator piezoelectric ladder filters
US3676806A (en) * 1969-11-06 1972-07-11 Gte Automatic Electric Lab Inc Polylithic crystal bandpass filter having attenuation pole frequencies in the lower stopband
US3613031A (en) * 1969-12-15 1971-10-12 Hughes Aircraft Co Crystal ladder network having improved passband attenuation characteristic
US3686592A (en) * 1970-10-08 1972-08-22 Us Army Monolithic coupled crystal resonator filter having cross impedance adjusting means
US3704433A (en) * 1971-05-27 1972-11-28 Bell Telephone Labor Inc Band-elimination filter
US4028647A (en) * 1976-04-28 1977-06-07 Northern Telecom Limited Monolithic crystal filters
US4099149A (en) * 1977-04-15 1978-07-04 Northern Telecom Limited Single side band monolithic crystal filter
US4163959A (en) * 1977-12-15 1979-08-07 Motorola, Inc. Monolithic crystal filter device
US4207535A (en) * 1978-03-20 1980-06-10 Motorola, Inc. Two-pole, fixed-tuned monolithic crystal frequency discriminator
EP0020729A4 (en) * 1978-12-11 1981-05-15 E Systems Inc MONOLITHIC CRYSTAL FILTER NETWORK WITHOUT INDUCTOR.
US4281300A (en) * 1979-11-08 1981-07-28 Motorola, Inc. Multi-pole crystal filter and method of improving the frequency response
US5051711A (en) * 1989-04-27 1991-09-24 Ten-Tec, Inc. Variable bandwidth crystal filter with varactor diodes
US5030934A (en) * 1989-07-05 1991-07-09 Motorola, Inc. Crystal notch filter comprising discrete quartz crystals coupled to a trimmable RC bridging network
US20080293668A1 (en) * 1995-01-27 2008-11-27 Schinazi Raymond F [5-carboxamido or 5-fluoro]-[2',3'-unsaturated or 3'-modified]-pyrimidine nucleosides
US20020167376A1 (en) * 2001-05-11 2002-11-14 Murata Manufacturing Co., Ltd. Piezoelectric filter

Also Published As

Publication number Publication date
NL66164C (en(2012)) 1950-03-15
CH215766A (de) 1941-07-15
FR858308A (fr) 1940-11-22
BE435676A (en(2012)) 1939-08-31
GB531662A (en) 1941-01-08
US2199921A (en) 1940-05-07
DE742179C (de) 1943-12-11

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